The Stink Bomb will be use to get the lady out of the detention and for you to go to the filling cabinet. The lady won’t go out there until you use the Stink Bomb.
How to Get the Stink Bomb
Go back to the school and go inside. Go into the Science Lab again. This time, click on the burner on top of the desk next to the test tubes. Turn the dial on the burner to 3. Now fill half the beaker with the blue liquid and then half with the yellow liquid. Once the beaker fills up, you’ll get a stink bomb!